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ON A FAST-TRACK: HUMAN dISCOVERy, ExPLORATION ANd SETTLEMENT OF SAHUL

Jon M. ErlandsonDepartment of Anthropology and Museum of Natural and

Cultural History, University of Oregon, Eugene OR 97403, USA

jerland@uoregon.edu

Recent decades have seen the emergence of new scientific

paradigms for the origins of anatomically modern humans

(AMH), a series of relatively rapid migrations that took these

people from Africa to the far corners of the world, and the role

of coastlines, boats and fishing in facilitating such dispersals.

These paradigm shifts all meet in Sunda, Sahul and western

Melanesia, where archaeology and anthropological genetics

are illuminating some of the earliest evidence for seafaring and

maritime migrations by AMH. The exact timing, routes and

adaptive diversity involved in such migrations remain to be

fully documented.

O’Connell and Allen argue that the peopling of Sahul was

an ‘archaeologically instantaneous’ process occurring between

ca 46,000 and 44,000 ya. They offer a ‘speculative model’ that

deals parsimoniously with numerous complex issues. I have no

qualms about rapid coastal migrations, as coastlines offer linear

migration routes, entirely at sea-level and with few geographic

barriers, often with very similar marine resources over vast areas.

For the Pacific Rim, Erlandson et al. (2007) argued that maritime

skills and similarities in the ecology of kelp forest and other

coastal habitats may have facilitated a rapid coastal migration

and colonisation from Asia to the Americas shortly after the end

of the LGM. A similar model could apply to the margins of the

Indian Ocean, where mangroves, coral reefs and other nearshore

ecosystems support a diverse array of similar shellfish, fish, birds

and marine mammal taxa from Africa to Asia and Australia.

I find nothing in O’Connell and Allen’s ‘fast track’ migration

that is not eminently reasonable. I agree that such a colonisation

process almost certainly involved relatively sophisticated

watercraft and seafaring capabilities. I also agree that maritime

immigrants would have spread rapidly into resource-rich interior

areas. Coastal habitats are partly terrestrial, after all, and coastal

peoples worldwide are well-attuned to subsistence opportunities

in the adjacent interior. As O’Connell and Allen note, moreover,

not all coastlines are equally productive, so those offering fewer

aquatic or terrestrial resources might have been skipped over

to focus on coastal sweet spots described by Bulbeck (2007)

and others. O’Connell and Allen’s model may overestimate the

vulnerability of estuarine ecosystems to sea-level fluctuations,

as intertidal organisms and communities tend by nature to be

highly resilient. During a critical period (ca 50,000-35,000 BP)

for their model, moreover, Pope and Terrell (2008:8) suggested

that estuarine habitats were relatively extensive in South and

East Asia.

O’Connell and Allen may be correct that the colonisation of

Sahul occurred very rapidly, but understanding a late Pleistocene

human colonisation of Sahul – as well as other Pleistocene

coastal migrations – is clouded by significant problems

(Erlandson 2001, 2010). First, the colonisation process took

place at, near, or just beyond the effective range of 14C dating,

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which reduces the confidence we can have in 14C dates from

archaeological sites, especially those run without the advanced

extraction, purification and measurement protocols essential for

dating samples of such age. Second, migrations from Sunda to

Sahul – primarily coastal and maritime in nature – took place

at a time when global sea-levels were ca 60-30 m below modern.

With sea-levels now at a 120,000 year high, vast areas of Sahul’s

coastal lowlands have been submerged by rising seas, including

most of the ancient coastlines early immigrants would have

traversed. Third, thousands of islands in Southeast Asia have still

seen relatively little research on Pleistocene archaeological sites:

a region that stunned the world with a relatively recent discovery

of Homo floresiensis may have more secrets to unveil. As a

result, I continue to teach my students that Sahul was probably

colonised ca 50,000±5000 years ago, an Aristotlean ‘golden mean’

that averages models by scholars who know much more than I

about the archaeology of the region.

There are some interesting parallels in O’Connell and Allen’s

model with a Clovis-First model for colonising the Americas

that is now in full retreat. Clovis-First advocates long argued for

a terminal Pleistocene terrestrial migration that settled North

and South America within roughly a millennium. They created

demographic models that were hypothetically possible, but now

are proven to have been wrong. Current archaeological and

genetic data suggest that the settlement of the Americas, which

may have involved a coastal migration and detours that saw

humans follow productive river systems deep into continental

interiors, took several millennia to accomplish. The American

experience, where two large continents now appear to have

been colonised, explored and settled within as little as three

millennia, could support O’Connell and Allen’s fast-track model

for colonising Sahul. One lesson learned from the widespread

distribution of Clovis sites in North America, however, is that

it took 2000 to 3000 years for pre-Clovis populations to reach

levels of archaeological visibility that also seem characteristic of

the earliest sites throughout Sahul.

Given some of the challenges alluded to above (drowned

shorelines, limited chronological resolution, lack of research

in key areas etc.), I hope the excessive conservatism of Clovis-

First models will not be repeated in Australia and Southeast Asia.

Given the active research and lively debate that continues on the

human colonisation of Sunda and Sahul, this seems unlikely. I

congratulate O’Connell and Allen on a fast track model for

the peopling of Sahul that is a reasonable hypothesis, one with

profound implications and numerous corollaries that provide

fertile ground for further research and testing.

SHOULd I STAy OR SHOULd I gO NOW? THE SPATIAL dyNAMICS OF FORAgINg ANd dIMINISHINg RETURNS

Brian F. Codding and Rebecca Bliege BirdDepartment of Anthropology, Stanford University, Stanford CA

94305, USA rbird@stanford.edu bcodding@stanford.edu

O’Connell and Allen should be praised for their concise and

focused synthesis of the debates and issues surrounding the

colonisation of Sahul. As they have done for the timing of this

event (e.g. Allen and O’Connell 2003; O’Connell and Allen 2004),

they now reframe the scope and direction of research towards

understanding how and why people rapidly entered the continent

and where they went. We would like to use this opportunity to

expand upon the theoretical framework presented in this and

companion papers (Allen and O’Connell 2010; O’Connell et

al. 2010), by examining foraging decisions across three explicit

spatial scales and proposing some additional archaeological

predictions within each.

At the heart of their model is the assumption that the rate

at which foragers can capture food diminishes with foraging

time (Charnov 1974): the more per capita time spent exploiting

a particular resource, remaining within a particular patch or

continuing to forage within a single catchment (sometimes

termed habitat), the lower the expected gains will be (see Figure

1). According to O’Connell and Allen, this is the engine that

drives people into and across Sahul: when resources are depleted,

people are better off moving into adjacent, unoccupied areas

than staying within depleted environments. However, the three

different models from which these predictions derive (prey

choice, patch choice and ideal free distribution) all operate at

explicitly different scales represented as resources, patches and

catchments, respectively. How these respond to population

pressure at these different scales, and how people then respond

to those changes will determine how, where and whether people

are expected to move. The effects of foraging on the environment

build cumulatively across these spatial scales, and devising

testable predictions about mobility patterns depends on the scale

at which foraging optimality is analysed.

Within a patch, foragers should pursue the highest ranking

resource to the exclusion of all others until the point when

continuing to search for that resource is less profitable than

taking the next highest ranking resource on encounter. As

encounter rates with higher ranked resources decline through

foraging-related resource depression, this results in an ever

widening ‘diet breadth’, leading to ever increasing handling costs,

but likely reduced search costs (Figure 1a). The prey choice

model predicts that people should respond to reductions in

high ranked prey with a reduction in mobility and a focus on

technological enhancements to reduce the costs of handling

lower ranked resources in patch, the standard model of resource

intensification. As O’Connell and Allen point out, there is little

archaeological evidence for ‘broad-spectrum’ intensification

in Sahul until the late Holocene, suggesting that foragers did

not tolerate in-patch declines for long. If, as they suggest, high

ranked but slow to reproduce rocky shore resources were driving

the decline, we should not necessarily see changes in species

composition, but are likely to see reductions in the size of staple

shellfish species over time.

If foragers decide not to remain and intensify their foraging

effort, they may abandon their patch and move on to exploit

other patches. These decisions are crucial if resources are

distributed heterogeneously across different patches. In these

circumstances, the critical foraging decisions involve which

patch-type to exploit and how long to stay within a particular

patch. With increasing consumption pressure, high ranking

patches would decline in productivity, leading foragers to enter

lower ranked patches (see Figure 1b). At the patch scale, foragers

expand their range within a catchment or habitat to encompass

patches of lower quality resources as high quality patches decline.

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Expansions in foraging radii are likely accompanied by increases

in logistic mobility, with people moving further to access more

remote patches, identifiable by the deposition of exotic resources

or raw materials acquired from patches located at a distance

from the central place.

As with resources and patches, increased human consumption

pressure should decrease overall foraging efficiency within

catchments (Fretwell and Lucas 1969), eventually causing

people to resettle in new areas (Figure 1c). Being the highest

spatial scale, these movements are significantly greater than

movements within or across patches. Given the marginal costs of

movement into adjacent territories that remain unoccupied, this

would likely result in the rapid dispersal of people as discussed

by O’Connell and Allen. Foraging decisions at this scale form

the backbone of O’Connell and Allen’s argument. As a next step,

we encourage the development of a spatially explicit ideal free

distribution model (e.g. Winterhalder et al. 2010), which would

rank catchments based on the aggregate returns and diminishing

gains within geographically specific patches according to the

expected resources within those patches. While such a model

has not yet been developed for any continent in any context,

it would provide detailed predictions about where the earliest

settlements are likely to occur and where we might expect greater

populations throughout time (Birdsell 1953).

Depletions at different spatial scales also likely occur over

differing temporal scales. However, in circumstances where there

are few opportunity costs to movement – as in scenarios where

people have watercraft – individuals will likely relocate across

vast distances in order to occupy highly ranked catchments.

This may appear as pulses and waves of settlement, with the

first settlers inhabiting higher ranking catchments, exploiting

the highest ranking patches within those catchments, and

pursuing the highest ranking resources within those patches.

Determining how these patterns encourage movement requires

building models incorporating individual decision-making to

test predictions at the largest spatial scales. O’Connell and Allen

have made great progress with this and companion publications,

and based on the available data, they are certainly correct. Next

steps will include further refinement of the model particulars

and tests of its predictions with new archaeological data.

FOUR qUESTIONS ABOUT FORAgINg MOdELS ANd THE PROCESS OF COLONISATION

Iain DavidsonIDHA Partners, 10 Cluny Rd, Armidale NSW 2350, Australia

iain.davidson@live.com.au

The target paper takes the debate about the narrative of

Australian archaeohistory a significant step forward, and sets up

some new research problems to be tackled.

O’Connell’s research with the Alyawara (Iliaura) (O’Connell

and Hawkes 1981) demonstrated that, despite their access to

purchased flour, modern fisher-gatherer-hunters will collect

seeds and grind them, provided there is an anthropologist who

can use a vehicle to drive them to the grasses. While this sounds

dismissive, it is actually very important for two reasons: (1) the

gatherers needed to know where and when the grasses were

suitable for harvest; (2) the anthropologist’s vehicle reduced the

cost of travel and search effectively to zero, altering the values

in the patch choice model. A distinguished ethnographer of

fisher-gatherer-hunters protested angrily about this work: ‘My

people do not forage optimally.’ I wondered, silently, whether

they were somehow more virtuous because they had not reached

optimality or perhaps they were somehow better than optimal.

This questioning also has implications: (3) are there behaviours

which do reduce the ‘optimality’ of foraging; and, (4) on what

time scales do the considerations of behavioural ecology have

to operate?

1. The Importance of InformationAll HBE/OFT models assume that the foragers have information

required to make the appropriate choices, and ethnography

demonstrates prodigious knowledge of plant and animal species

(e.g. O’Connell et al. 1983), as well as key indicators of seasonality.

Golson (1971) showed that there were some similarities between

the vegetation communities on either side of the Wallace Line,

but only small numbers of species familiar to initial colonists

of restricted distribution within Australia. New colonists needed

to acquire information about the nature of suitable resources,

especially as some contain toxins, whatever their means of

dealing with them (e.g. Beck 1992).

As a result of this uncertainty about information, O’Connell

and Allen are right in the way that Bowdler (1977) was right:

the easiest option was to focus on familiar resources that were

present on both coasts. As coastal populations expanded, so there

Resources

Patches

Catchments

- Population Impact +

- O

vera

ll Fo

ragi

ng R

etur

ns

+

12

3

1

2

3

(a)

(b)

(c)

Figure 1 Predicted foraging dynamics across each spatial scale: (a) in patch; (b) between patches; and, (c) across catchments. The arrows indicate the point at which foragers should switch to alternative resources, patches or catchments.

20 Number 74, June 2012

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was pressure to move inland; water and its variable availability

was the chief limiting factor in many regions (cf. White and

O’Connell 1982:51).

The first colonists of any region needed information on plant

species, including variation in their availability and food yield.

New colonists needed to discover what the resources were, as

well as their relative value. Both availability and ranks of food

resources could change stochastically from season to season, year

to year and decade to decade, as well as biozone to biozone. In

the fullness of time, such information could be obtained, but,

as oral histories seem to suggest, passing on information about

variation was difficult when the time scales of variation were

longer than individual experience (Davidson 1992).

2. The Costs of ForagingThere are also hidden costs of foraging, such as the embedded

cost of O’Connell’s vehicle. These feature in the discussion

of risk reduction in Australian archaeohistory deriving from

the work of Oswalt (1976), who characterised technologies

in terms of the number of technounits. Oswalt’s fallacy is

exposed by his equating of a digging stick and a chimpanzee’s

termiting wand because they are both single sticks (McGrew

1987). The digging stick, unlike the termiting wand, requires

stone tools to make it and can be used many times. So, one of

the costs of human foraging is not only about food sources,

but also acquiring information about, and obtaining, stone for

tools. It is noteworthy that at Sandy Creek 1 in Cape York, the

earliest assemblages (ca 37 cal ka) were made on quartz crystal

(Morwood et al. 1995), as if the first people had not yet found the

raw material sources they later relied on.

3. Are there Adaptive Behaviours that Reduce the Optimality of Foraging?

Historically, symbolically supported sets of relationships and long

distance interactions were part of the mechanism by which such

uncertainties were dealt with, a process that began early (Veth et

al. 2011). This could have been a disadvantage, particularly by

defining ritual relationships with place that may have endured

beyond the time that such places were sweet spots. Given that

rock art of all ages, and much of the symbolic expression of

relationships in the historical period, involved relationships

with animals (and much less with plants), such expressions of

value might affect assessments of resource ranking. In addition,

early beads suggest symbolic marking of interpersonal relations

that could promote the adaptive success of populations that

differentiated in such ways (Boyd and Richerson 1987).

4. On what Time Scales does Behavioural Ecology Operate?

At some level, the sorts of decisions O’Connell and Allen address

are almost encapsulated by the choice of restaurant alluded to

in their title, but human behaviour was subject to many more

selective pressures than those individual choices. As people

exhausted resources or populations became too big for the

resources of the region, they could have moved on or targeted

lower ranked resources, perhaps becoming strategic generalists.

Symbolic attachment to places probably tethered some groups

who adjusted to the stress of variations in resources and gave up

the option of seeking higher ranked resources in the restaurant

over the next sand hill. Sometimes they failed, as the patterning

of radiocarbon dates suggests, but in the end they found ways to

cope with the scale of variation that the environment threw at

them (Davidson in press).

COMMENT

Tom D. DillehayVanderbilt University, 211 Kirkland Hall, Nashville TN 37240, USA

tom.d.dillehay@vanderbilt.edu

O’Connell and Allen have provided an articulate,

multidimensional model of a subject made complex by its

interdisciplinary nature, its long history of debate and the

continuing shortage of hard archeological evidence for many

regions. I would like to expand briefly on some of the more

general archaeological and anthropological aspects of the model,

which are necessarily dealt with rather cursorily in the review.

O’Connell and Allen discuss the implications of an

archaeological record defined primarily by infrequent, short-

term occupation sites produced by small, highly mobile groups.

They also infer that human populations were generally ‘small and

patchily distributed across Sahul’. Not discussed by the authors

are the implications of this record for the absence, or minimal

presence, of more complex hunter-gatherers at the end of the

Pleistocene period. In other continents, the relationship between

late Pleistocene plant communities and humans, for instance,

often laid the developmental foundations for long distance

social networks, reduced territoriality if not semi-sedentism, and

eventually plant domestication. In the northern Peruvian desert

and surrounding environs during the late Pleistocene, foragers

were experimenting with new food procurement strategies,

occasionally rejecting some or all of them, and then returning to

prior ones (Dillehay 2011). Although the archaeological record

of this region indicates short-term site occupation similar to

that described for much of Sahul, it also reflects continuous

use of the same habitats over several millennia, as evidenced by

repeated yet ephemeral occupation of the same site locales. Some

foragers even managed plant and animal resources by fostering

environmental conditions (e.g. perhaps intentional burning or

predator overkill) that promoted preferred foods. This certainly

was the case for palm nuts in the Amazon rainforest and for

shellfish along the Pacific coast of South America. Is there any

evidence of incipient foraging complexity or early resource

management in Sahul at the end of the Pleistocene, and, if so,

how might they have impacted patch choice, marginal value and ideal free distribution?

Although the O’Connell and Allen model is focused on

various concepts developed within optimal foraging strategy, I

wonder why the social aspects of late Pleistocene humans are not

discussed as possible factors influencing resource exploitation,

diet choice, site patterning and so forth. For parts of South

America, we can now infer that social fissioning was probably

less common than we had thought and that it occurred when the

local carrying capacity had been exceeded or social tensions were

high. When it did occur, which probably resulted in smaller social

units moving around the landscape, we suspect that splinter

groups maintained close ties with previous groups for economic

support and social interactions. We now understand that some

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early foraging societies institutionalised practices that served

additional (and diverse) functions for their individual members

and which were organised as relatively specific entities in

different places (e.g. Rowley-Conwy 2001). These practices were

ritual orders, social networks, technological traditions, perhaps

gender-based units, and others that were performed in specific

private or public places, such as individual huts or rock art sites.

Given the rich rock art of many areas of Sahul, can anything be

inferred from it regarding early social and behavioral patterns?

A point I find intriguing relates to diet breadth and the

complexity of technology. The review notes that a bifacial stone

tool technology (and other technologies?) may have been lost

en-route from Africa and South Asia to Sahul ‘due to a series of

demographic “bottlenecks” that ultimately reduced the cultural

transmission and thus the technological repertoire of early

colonisers.’ Rather than imposing cultural transmission as a

causal factor here, O’Connell and Allen suggest that diet breadth

and technological complexity may correlate to explain the lack

of diversity/complexity in late Pleistocene stone tool industries.

They argue that a wider diversity of exploited resources increases

‘handling time’ and procurement techniques, which leads to

greater technological complexity. In South America, the reverse

seems to be the case: simple and less complex unifacial industries

are generally correlated with broad-spectrum diets derived

from large and small game hunting and the gathering of a wide

variety of plant species. These diets required more handling and

allocation time and procurement strategies across many different

environments. The primary adaptive technology for these diets

was a unifacial industry, which provided tools used for a wide

variety of handling and other functions. More complex and

diverse technologies, on the other hand, are associated with

specialised game hunting. Further, the general pattern in Peru

was ongoing frequency shifts in the use of alternative adaptive

strategies that incorporated changes in the use of different

technologies and tool types (stemmed and fluted point and

unifacial industries) in different time periods and in different

ecological settings.

Along similar lines, it seems that bifacial technologies were

occasionally ‘lost’, or at least less diversified, as late Pleistocene

people spread through Central America and into the wide range

of environments in South America. But there are archaeological

records across the continent suggesting that these technologies

were both lost and recovered from time-to-time. We do not

know if the lost, narrowed or recovered technologies relate to

cultural transmission, but, if so, we need to examine early social

networks and how information was passed along them, and

whether ‘technological diversity is likely more a function of

ecological context and foragers’ intellectual solutions.’ This topic

requires more inter-continental comparative research.

COMMENT

David HortonIndependent Scholar drhorton@optusnet.com.au

There is much to like in this paper, such as putting together all

the most recent research and applying it to the age old problem

of trying to define the timing and nature of the first colonisation

of Australia. When Birdsell, and even when Bowdler and I,

considered the subject in necessarily broad terms, there was far

less data than there is now.

I am also delighted to see recognition of the importance

of climate change, and the dismissal of firestick farming and

megafaunal extinctions nonsense. It is long past time Australian

archaeology left these ancient shibboleths behind. They have

been a drag on the discipline, preventing the analysis of new

data in ideologically uncluttered ways. Worse, they have led to

the great increase in prescribed burning, and to an inability to

use past climate change as an analogue, and a warning, for what

the country faces as the planet warms.

But, and there must be one, I do have a general problem with

the paper. Many years ago Mortimer Wheeler famously said ‘as

for archaeology, I do not know whether it is to be considered

an art or a science’ (1954:50). The problem here, I think, is too

much science and not enough art. Humans are not rabbits, or

fruit fly, or yeast.

Humans use the most productive patches as a high priority

then move to the next most productive and so on? Well,

they might, I suppose, with perfect knowledge and a rather

mechanical view of ‘diet’. Or more likely they won’t, depending

on actual group composition, religious considerations,

food preferences, seasonal variations, local water resources,

shelter availability, relationships with neighbouring groups,

topography, cultural matters, storage technology, gathering

and hunting technology and so on. I don’t think ‘patches’ are

as important as the overall human habitat available, which is

why I thought, and still think, that the slopes and plains of

northern and eastern Australia are a likely initial pathway. The

beaches look good to us, but for a hunter-gatherer without

watercraft I think probably not so much. Sure you can strip all

the shellfish off rocks and dig for them in sand, but then what?

Where is the handy freshwater and shelter that doesn’t face

towards the storms, and topography that allows easy movement

inland? Conversely, these days it is easy to underestimate the

biodiversity and favourable environment of the slopes and

plains, seeing it, as we do now, in its relatively sterile form.

From 1813 on, with the Blue Mountains crossed, these slopes

and plains, so favourable for grazing and later other farming

practices, were subject to rapid, and far greater, change than

elsewhere in the country. Trees were cleared enthusiastically to

expand grazing grass, the hooves of sheep and cattle trampled

the soil, weeds took hold, pastures were fertilised and improved,

fences erected, native animals hunted, creeks dammed, rivers

silted up, and foxes, rabbits, sparrows and honey bees arrived.

The largely bare open hills I see from my window are as much

an artefact of British farming as are the similar hills in England

and as unappealing for Aboriginal occupation now as they

would have been appealing 200 years ago. I think both beach

and semi-arid areas, as permanent settlement areas, were only

occupied as population built up in the woodlands of slopes and

plains and the excess had to spread out further.

This brings me to population. As Allen and O’Connell point

out, there is no evidence for the Birdsell-type calculation that

sees population growing very rapidly from Adam and Eve to a

million in no time at all as it grows exponentially through the

generations: One, two, many … like yeast in a test tube. But it is

human beings involved here, living in groups, with social, cultural,

spiritual, historic, psychological, ecological, physiological and

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structural limitations and advantages, not to mention the effects

of natural disasters. I don’t think any human groups are likely to

increase at the maximum possible rate, nor do I think Aboriginal

groups in different parts of Australia are all going to increase at

the same rate.

Finally, another problem the authors are well aware of.

Projecting our current image of what the present-day Australian

environment is like back into even the recent past, let alone

the distant past, is very misleading. Applying the ethnography

of a handful of well-studied Aboriginal groups from this

very atypical period since 1788 even to other contemporary

Aboriginal groups is fraught with danger. Applying it to, say,

European Mesolithic hunters is even more inappropriate. And

it is equally true that applying what we learnt about Yolgnu,

Warlpiri and other groups in the 1960s and 1970s to the

ancestral ‘Aborigines’ of 40,000 and more years ago simply

assumes what needs to be proved. This is a self-fulfilling

prophecy as damaging as that of fire-stick farming.

This paper is a fine contribution to the ‘Origin of the

Australians’ genre and I congratulate the authors. It is another

step along a way which really relies much more on small steps

than big leaps – much like the colonisation of Australia I suppose.

NOW BRINg ME THAT HORIzON

William F. KeeganFlorida Museum of Natural History, University of Florida,

Gainesville FL 32611, USA keegan@flmnh.ufl.edu

Archaeologists seem to face far more complications in making

the crossing to Sahul than the people who accomplished this feat

about 50 kya. Radiocarbon dates are now so numerous that the

presence of humans in Sahul at this early date cannot be ignored.

The question is how and why this passage was accomplished. In

answer, O’Connell and Allen present a very logical argument.

Reconstructing the crossing to Sahul focuses initially on the

availability and type of watercraft. I do not see this as a major

problem. Most large rivers dispatch substantial quantities of

floating debris, including large trees (Keegan and Mitchell 1986).

It is hard to imagine that modern humans, even 50 kya, did not

understand buoyancy. It is relatively easy to construct a raft that

can navigate calm waters (and often are flexible in rough seas1).

Sahul may have been discovered by accident, but accident had

nothing to do with its colonisation.

We face similar issues in the Caribbean (Keegan in press;

see Figure 2). The first evidence for humans in the insular

Caribbean comes from the Greater Antilles, with the earliest

dates clustered around 7 kya. The initial colonists were mobile

foragers who exploited chert sources in the islands and may

have been responsible for the extirpation of sloths and manatees.

Unfortunately, all of the sites from this time are lithic scatters with

no faunal remains. This example is relevant to the colonisation of

Sahul because in the Caribbean people with similar practices did

not cross the shortest water gaps. Based solely on geographical

distance we would expect the first colonists to have crossed

from Florida, the Yucatan or Trinidad. Yet the material evidence

indicates that the first colonists, and the second wave, came from

1 see http://balseros.miami.edu/introduction.htm

the ‘Intermediate’ or Isthmo-Colombian area (Keegan in press).

Expeditions to colonise the islands involved crossing an expanse

of the Caribbean Sea by peoples we assume to have limited

maritime technology (Figure 3).

Efforts to explain the development of watercraft that

were substantial enough to make the crossing to Sahul have

emphasised the exploitation of marine resources. O’Connor et

al. (2011) recently used faunal evidence from the Jerimalai site

in East Timor to highlight the exploitation of coastal and pelagic

resources ca 42 kya. I am not convinced that watercraft were

necessary. Intertidal molluscs are on dry land for ca 12 hours

each day, and many reef species can be collected by walking along

the reef at low tide. Second, Scombridae (tunas), which they

designated as pelagic, actually frequent shallow coastal waters as

juveniles. Given the climatic variations described by O’Connell

and Allen, these Scombridae may not be pelagic. Generalised

marine habitat denominations for taxa do not capture the

behavioral ranges of fishes (Keegan 2009). Nevertheless, this

line of reasoning does suggest a motive for the production

of watercraft.

O’Connell and Allen adopt a similar, but more operationalised,

perspective in their application of optimal foraging theory (OFT).

I agree with their reasoning, which enhances our understanding

of why particular patches were targeted. The issue I have is that

OFT focuses on marginal and average return rates, and ignores

total return rates (Keegan 1986). The marginal return rate is

optimised to achieve a goal, which is defined as enough food to

meet quotidian requirements (total returns or demand). If the

pursuit, capture and handling of additional prey will not provide

a consumable yield, then there is no need to invest additional

time in searching for prey.

Furthermore, if mobile foragers were the original affluent

society, then they had an abundance of time. After foraging

goals were met, foragers had to decide what to do in their ‘free

time’. The possible options are too numerous to mention, but

one option was the collection and consumption of non-optimal

comestibles. Most molluscs have an incredibly low marginal

return rate, yet they are found in coastal and inland sites

throughout the world. In my opinion, the consumption of small

molluscs is an expression of wealth. People eat small molluscs

because they have the luxury, and not the need, to do so.

Figure 2 The timing and location of human migrations in the insular Caribbean (Keegan in press).

23Number 74, June 2012

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OFT provides a formal economic structure to the most basic

daily decisions in people’s lives. Foragers should expand diet

breadth during periods of abundance (high total returns from

the highest ranked foods) by experimenting with non-optimal

foods. Such experimentation can be achieved at relatively low

opportunity costs. In contrast, diet breadth should contract

during periods of stress (e.g. the colonisation of new territories)

because the search for, and pursuit of, the highest ranked foods

in the optimal set offers the most reliable diet (measured in

terms of marginal return rates). Thus, the earliest sites should

reflect a focus on the highest ranked items, such as at the Coralie

site (Keegan 2007, 2010).

The distribution of patches and prey types promotes

dispersion. This centrifugal force is countered by the distribution

of people; a centripetal force that promotes mobility for

the purposes of assembly. O’Connell and Allen are right in

highlighting demographic parameters, and I agree that the

colonisation of Sahul was accomplished by ‘several separate

landing parties’ that maintained contact, that at the very least,

allowed for the exchange of mates.

The missing element in their argument is social

organisation. A small group colonising Sahul may have

been demographically viable, but was it socially viable? All

societies have marriage conventions. The rapid movement

into Sahul, followed by an abrupt stop, probably reflects the

accumulation of a social population sufficient to allow the

socially constructed exchange of spouses without requiring

return voyages to Sunda. Social relations established through

the exchange of spouses require reciprocity (e.g. Jordan et al.

2009; Keegan 2010). Colonisation involves the movement of a

collectivity of individuals who are members of multiple social

groups and who require intercourse with their parent groups.

Island colonisation is not unidirectional.

O’Connell and Allen present a strong case for the biological

imperatives that structured the colonisation of Sahul. What is

missing is a consideration of the social imperatives. Seaworthy

vessels facilitated the exploitation of new areas and the

colonisation of Sahul, but their invention was predicated on the

need for social interactions. Humans developed watercraft to

facilitate contact with other humans, and not solely to permit

the exploitation of marine resources.

COMMENT

Richard CosgroveArchaeology Program, La Trobe University, Bundoora VIC 3086,

Australia r.cosgrove@latrobe.edu.au

O’Connell and Allen propose one of the more structured

archaeological colonisation models of the recent past. They

present a theory of colonisation based on the available

palaeoecological and archaeological data from the earliest

part of the Sahul record. They suggest that their model can be

tested and refuted. If so, it is a key element in any judgement

of the predictive power of a model. It is an advance on earlier

attempts, such as Birdsell, Bowdler and Horton, to explain

the settlement process of Sahul. At least O’Connell and Allen

cartographically recognise that New Guinea and Tasmania

were in fact connected to Australia at that time. Further, some

earlier models were largely immunised against testing. For

example, Bowdler (1977) in her coastal colonisation model

observed that many, if not all, of the earliest sites were now

under the ocean. Fortunately, later discoveries of sites like

Bobongara, Matenkupkum and Matembek, that continued to

be tectonically uplifted over the last 40,000 years, beyond the

highest sea-levels, preserve a record of human behaviour that

remain unaffected by submergence. Indeed, late Pleistocene

sites discovered before 1977 like King’s Table, Kisope, Kenniff

Cave and Koonalda Cave, suggested an altogether different

adaptation process to the one offered up by Bowdler (1977).

What is clear, however, from the contemporary Australian

archaeological data is that its range and variety have become

more complex, both in time and space, so the developments

of explanatory models require a more sophisticated approach.

This paper tackles the newer evidence, although the usefulness

of their model is constrained by some inappropriate

scalar comparisons.

Models are abstractions of reality that should specify the

expected range of attributes used at various scales that can

identify the archaeological correlates of human behaviours.

O’Connell and Allen could have better dealt with this issue,

explaining the links between the various scales of the observed

phenomenon and archaeological processes as identified in the

data sets. The use of ethnographic analogy is not a problem in

itself and they admit that these are only guiding principles. Their

assumptions are explicit, such as certain behaviours like ranking

food, obtaining mates (and keeping them), and social interaction,

which almost certainly took place in the past. However, there is

a lack of sufficiently strong analogy to link the different scales of

observation together.

For example, their model is based on small scale

ethnographic observations that assume that some common

hunter-gatherer behaviours are likely to be embedded in the

archaeology. However, for their model to be useful, predictions

must be made at commensurate scales between the observed

and predicted archaeological, ecological, climatic and

environmental phenomena. Identifying these is difficult, since

a much higher resolution chronology from all early sites is

needed for comparisons, not just climatic data. Their model

does not sufficiently discuss its limitations, especially the fact

that not all early sites can be commensurately compared given

Figure 3 Modern Haitian ‘pi pris’ used for coastal fishing (relevant to OFT its name can be translated as ‘small price’). It is similar to rafts that made the 200 km crossing from Cuba to Florida (from the north coast), and the 400 km crossing to the Cayman Islands (from the south) in 1994 (photograph courtesy of Lisabeth Carlson).

24 Number 74, June 2012

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the variable structural properties of each record. It is noteworthy

that a majority – 63% – of their archaeological data come from

rockshelters of various geologies.

This is crucial if, for example, the ‘narrow diet’ hypothesis

of early colonists is to be supported. How ‘narrow’ is ‘narrow’?

Detailing preservation conditions and site similarity are as

important as identifying specific taphonomic differences

that structure the archaeological evidence. Their discussion

of ‘subsistence and diet breadth’ importantly includes plants,

but, because evidence of plant use is rarely found, predictions

about narrow diet breadths are difficult to make. This limitation

compounds the difficulty of testing their model in any

meaningful way so that the essence of a good model is lost.

Some of the conditional elements in the argument, such as

colonisation and climate change, are discussed at both small

(human response time) and large (Marine Isotope Stage) time

scales. The ‘Archaeological Assessment’ section is problematic,

as only the earliest dates are described. Significantly, other

chronological markers of change and associated material

culture need to describe the process by which settlement took

place and can be understood. In other words, what are the range

of archaeological attributes needed to identify the behavioural

responses and how are these to be tested given the scalar

problems of the data?

In their ‘simple scenario’, O’Connell and Allen hypothesise

that human groups were small, highly mobile and focused

on ‘sweet spots’. These foraging locations, once depleted of

high ranked resources, were abandoned, with human groups

moving to the next location rather than to the next lowest

ranked resource in that location. Identifying such processes is

again a scalar problem in the model, since the archaeological

predications must be made at levels of human responses, not

large scale climate cycles.

Further, sweet spots are where it is argued people pulse

out in the good time and retreat in the bad. These sweet spots,

however, will be equally affected by climatic downturns and

become rather sour spots to live, with populations taking a hit.

As is known, it’s the bad times that control population levels.

The point here is that there is a wide range of geographic

variability across the 11.5 million square kilometre Sahul

continent. The variable effect of modern drought over regional

areas of Australia is something that could be expected in the late

Pleistocene but perhaps of higher frequency and magnitude.

O‘Connell and Allen seem to fall into the trap of assuming

similarity across this vast Sahul continent in terms of climatic

impact, although archaeologically it is quite variable during

the LGM. However, as they recognise, it’s the embedded small

scale, ENSO-like perturbations that dictate population levels.

Thus, momentum for post-drought mobility will be linked

to recovery rates of both population and the palaeoecology.

Modelling the predicted archaeological patterns in both space

and time is dictated by whether group relocation or accessing a

lower ranked food can be identified archaeologically elsewhere.

At this point we are back to the problems of scale and the

resolving powers of the different records.

Overall it’s a positive attempt at model building. At least it

has a greater level of detail, specificity and predictive power than

other pan-continental model building attempts of the past.

THE SHIPPINg NEWS

Ian LilleyAboriginal and Torres Strait Islander Studies Unit, The University

of Queensland, Brisbane QLD 4072, Australia i.lilley@uq.edu.au

Joe Birdsell was a clever chap. He has had some bad press over the

years, but I don’t think it is really deserved. This paper gives us

another reason to dust off Birdsell’s reputation, as O’Connell and

Allen return to a proposition he raised 35 years ago, namely that

colonisation of the continent was effected with boats that were

more sophisticated than those recorded ethnographically. In a

related paper they published with Hawkes in 2010, O’Connell

and Allen drew attention to Birdsell’s deduction, but not here,

even though for other reasons they cite the chapter in which

Birdsell made the point. It may seem inconsequential in the

greater scheme of things, but we in the Birdsell Liberation Front

are always watching ...

On a less flippant note, this paper (and indeed Birdsell’s

original chapter and the writings of others on the topic of

early Australian watercraft) raises a persistent question for us:

the extent to which ethnographic analogy helps or hinders

archaeological analysis and interpretation. The discipline goes

back and forth on this issue without resolution, and as much as

I agree with the thrust of O’Connell and Allen’s present paper, it

seems to me that they want to have it both ways when it comes

to the use of ethnographic examples, without any explanation of

why they think it’s justified to do so.

The accumulating empirical evidence for the use of capable

ocean-going watercraft in and around Sahul 40,000-50,000

years ago may confront our crustier colleagues, but it seems

incontrovertible. This in turn has major implications for the

initial movement of modern people out of Africa around the

Southern Dispersal Arc, and all of it shines a very strong light

on orthodoxies concerning human evolution and progress.

This is truly exciting stuff! Yet if we are turning things on their

heads in this way and, like O’Connell and Allen, explicitly ‘reject

inferences ... that rely on assumptions about marine technology

constrained by the Australian ethnographic record’, we have to

ask why we still rely on ethnographic analogy as heavily as they

do in other parts of this paper. If the boats were different back

then, why assume that what was true of ethnographic subsistence

and settlement patterns ‘was also true for early Sahul colonisers’?

Why assume ‘foraging options ... were similar to those reported

historically’? And so on, whether regarding women’s roles,

population growth and density, or diet breadth.

I know we have to start somewhere, analytically-speaking,

and O’Connell and Allen have certainly been clear about the

assumptions they are making in this regard. As a discipline

we’ve been insisting for a while now, though, that the past is

a foreign country where they did things differently. It seems

inconsistent to be so forceful about boats in this regard, but to

make no comment about how appropriate it might be to use

analogies in the other instances. This is especially true of matters

concerning subsistence and settlement if, as O’Connell and Allen

contend, ‘human populations ... remained much smaller than

sometimes imagined’, and thus presumably also much smaller

than the ethnographically-recorded (or at least guesstimated)

populations whose foraging and habitation patterns underpin

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the authors’ optimal foraging approach. The authors themselves

seem to confirm this point when they note that ‘Historically

known patterns of economy, technology and demography

emerged only in the Holocene’.

Where to from here? I understand, and am philosophically

inclined towards, the critique of inductive reasoning O’Connell

and Allen made with Hawkes in 2010, which is behind

their willingness to use ethnographic analogy in deductive

theoretical models. As their own work demonstrates in this

paper, though, it is induction from facts emerging from the

ground in places such as Timor and the Bismarck Archipelago

that is forcing the issue with boats. This is not the place for

extended methodological discussion, but clearly we need

to move beyond what are now very stale arguments about

deductive vs inductive reasoning. Quality scholarship usually

entails a mix of both, in proportion to the nature and quality

of one’s empirical data, the internal logical consistency of

one’s deductive theoretical models, and the fit between one’s

data and one’s models. Despite their seemingly hard-nosed

rhetoric, this is pretty much what O’Connell and Allen do

in this paper. Deductive models can be based on almost any

sort of information, including potentially quite misleading

ethnographic analogy. One needs to make one’s sources of

such information clear. This the authors do. One should also

make explicit the limitations of that information, in this case

ethnographic analogy, which they don’t (unless it’s about

boats). I may have become a bit obsessive about it, but in the

end the omission really detracted from my reading of the paper.

dANCINg ON PINS: TENSION BETWEEN CLEVER THEORy ANd MATERIAL RECORdS IN AUSTRALIAN ARCHAEOLOgy

Peter HiscockSchool of Archaeology and Anthropology, The Australian

National University, Canberra ACT 0200, Australia

Peter.Hiscock@anu.edu.au

Thomas Aquinas (ca 1225-1274 AD), like many medieval

philosophers, explored the nature of his world through detailed

theorising – building models through logic and dialectic. This

model building was focused on the consequences of phenomena

believed to exist, with an emphasis on the exercise of reason

but not of empiricism. Consequently, although Aquinas was a

crucial contributor to modern thinking, his theorising involved

questions as abstruse as whether there was defecation in Paradise

or whether angels were material entities (often misquoted as how

many angels could dance on the point of a pin). Those medieval

debates displayed impressive intellectual dexterity, but in

retrospect we can view the sophisticated thought as squandered

on illusory concerns and fantastical visions of the world.

Comparable situations occur repeatedly in science, because

diagnosing what happens in the world can be extremely difficult.

Perhaps, as we archaeologists always claim, it is more difficult

to interpret the human past from material residues than to

do many other kinds of science. In any case, tensions between

explanatory theory and the inferred pasts that are the subject

of those explanations have occurred throughout the history

of archaeology. The issue is not that explanatory models are

eventually refuted but that, at the time they were proposed, they

sought to explain impressions of the past which were empirically

dubious or even demonstrably incorrect. A well-known instance

of this was Bowdler’s (1977) coastal colonisation model, which

at the time it was formulated was already contradicted by inland

sites such as Kenniff Cave. Currently, the same tensions are

displayed in the extended debates over whether the temporal

coincidence between the arrival of humans and the extinction

of megafauna is evidence of human culpability, despite the

uncertainty about the timing of either arrivals or extinctions

and the existing inability to adequately test human contributions

(see Field and Wroe 2012). Of course these tensions can be

extraordinarily productive, driving scholars to collect further

data and to reconceptualise their analytical framework, but

creative outcomes are most likely when scholars acknowledge and

engage with the uncertainty and interpretative disagreements.

In this interesting paper O’Connell and Allen offer

explanations that are both elaborate and novel for past cultural

events and processes. The use of principles from behavioural

ecology, and specifically OFT, is intriguing and clearly

worthwhile. These approaches to understanding behavioural

decisions are known to be powerful and will have intuitive appeal

to researchers in the field. It is therefore of considerable value

that they have chosen to explore the colonisation of Sahul in this

way. My concern here is not with the application of ecological

perspectives to the range-expansion of humans, since that

seems both appropriate and inevitable, but to the question of

what is being explained. In presenting their analysis they discuss

archaeological data that supports a particular image of the

colonisation process, specifically a late, rapid dispersion of Homo

sapiens from Africa to Australia, scattering in low population

densities, using only simple technologies across the continent

and being subsequently largely isolated. Such an image is, and

should be, contested. Certainly O’Connell and Allen (2004) have

given their reasons for advocating a late date for colonisation, but

the reconstructions of the colonising event by other researchers

do not accord with theirs, and the evidence is clearly arguable.

Certainly many of the components of the colonisation story told

by O’Connell and Allen should be considered carefully. I alert

readers to some of the obvious claims they may wish to consider.

The Colonisation of Sahul Occurred 44-46 kya? This assertion ignores sites that have older dates claimed to be

in association with cultural material, and fails to account for

the sampling issues in investigating the archaeological record.

Furthermore, it does not reflect the dating uncertainties of

sites such as Parkupirti which may be older than 40 kya, but

how much older is currently very poorly defined. Additionally,

I and others have repeatedly made the case that the oldest sites

found, especially in the south and inland of the palaeocoast,

are not likely to date the arrival of humans but more likely

reveal the time when population and landscape use had

risen to the point of being archaeologically visible. So even if

claims for earlier sites are eventually rejected and O’Connell

and Allen are supported in their assertion that uncontested

dates for Homo sapiens fall in a relatively narrow time range

(44-46 ky BP), this must be considered a time when humans

have established themselves across Australia, not necessarily

26 Number 74, June 2012

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the time at which colonisation occurred. Consequently,

assertions about the timing and rapidity of movement and

the relationship of that movement to sea-level movement are

speculative at best.

Occupation in the Early Millennia Involved Infrequent, Short-Term Occupation by Small, Highly Mobile Human Groups?This oft-cited claim is usually based, as it is in O’Connell and

Allen’s paper, on the discovery of sites that are individually small

in area and/or low in perceived artefact discard rates. While this

might be a consequence of small groups staying only for short

times this literal interpretation is not without its uncertainties.

Critical questions remain largely unanswered, such as what

proportion of early occupation took place inside rockshelter sites,

what proportion of early occupation sites are preserved, and

what selection of archaeological sites have been recovered (see

Langley et al. 2011). At any time period the interpretation of site

numbers and sizes in terms of population and residential group

size and mobility is tricky (see Attenbrow 2004), and for the

earliest period of human occupation I suspect more discussion

will be required to resolve what interpretations are sustainable.

Early Sahul Technology was Simple and Displayed Limited Variation through Time and Space? It is unfortunate that the authors do not elaborate and

substantiate this statement, for it is contrary to my impressions

of the evidence (see arguments in Hiscock 2008). Not only are

the technologies revealed in early assemblages of flaked stone

artefacts quite diverse across the continent, we now have evidence

of bone and shell working creating tools/ornaments and of the

production of edge-ground axes at or before about 40 kya. Using

the late colonisation chronology advocated by O’Connell and

Allen these data indicate a geographical and temporal diversity

of technologies immediately after the dispersal of humans

across the continent. Additionally the notion of simplicity is

undemonstrated, and relies on out-dated depictions of stone

assemblages that have long been challenged. O’Connell and

Allen conclude their paper with an admission that the pelagic

fishing, and the elaborate gear that probably supported it, is

hard to explain in their model. Indeed that does merit further

investigation, because it is one possible pointer to a colonisation-

era cultural system in which population might have been greater

and empty territory often less available than their model implies.

These are just a few of the inferences about the past that

O’Connell and Allen present and attempt to explain. Each

is debatable and warrants investigation, because, while the

ecological approach applied in the paper is intriguing, if it

is applied to visions of the past that are more fantastical than

evident, it too may be squandered.

BOATS, STONES ANd RISKS

Robin TorrenceAustralian Museum, 6 College Street, Sydney NSW 2010,

Australia Robin.Torrence@austmus.gov.au

This interesting model combines evolutionary ecology with the

prime mover of population pressure invoked to kick off the

human colonisation of Sahul. I question whether population

pressure was necessary to ‘push’ groups only targeting resources

with high returns. More likely, once they left Africa, colonising

populations would have been ‘pulled’ by the high ranked

resources in adjacent unoccupied land and seascapes. Given the

nature of tropical environments, especially in Sahul, such food

sources tend to be relatively sedentary (e.g. plants, molluscs,

varanids and arboreal mammals). Their rapid depletion would

necessitate frequent moves, which may help explain the use of

boats, especially because these could reduce the stress of constant

mobility on women and children. Marine technology would

be better incorporated into the model by acknowledging its

initial role as transport required by a subsistence focus on high

return resources, rather than for fishing, which is perhaps better

conceived as a by-product.

Continuing the theme of technology, the authors rightly

attack northern latitude scholars, such as Mellars, who continue

to make simplistic, direct links between the evolution of human

intelligence and the nature of stone tool assemblages, despite

the contradictory archaeological record of Homo sapiens in

Sahul which is dominated by a simple flake-core technology (cf.

Brumm and Moore 2005). Instead, O’Connell and Allen try to

show that a better way to explain human behavior is to study

the relationships between ‘the ecological context and foragers’

intellectual solutions to the problems of making a living’.

Whereas I agree that the particular configuration of stone

technology is the consequence of people finding optimal

solutions to problems posed by both their physical and social

environments (Torrence 1989), I run into difficulties with the

specific hypotheses they put forward, although I appreciate these

are preliminary attempts to exemplify their proposed approach.

Accurate definitions underpin all good modelling. Tools

and technology refer to very different entities. Technology

encompasses ‘physical setting, social context, actors, knowledge,

energy sources, raw materials, tools, actions and outcomes’

(Torrence 2001:74; cf. Bleed 1997). Boats are not necessarily

‘complex’ tools, but the knowledge and skills required to navigate

across the ocean may be very sophisticated. Does this mean that

pelagic fishing is necessarily more complex than the behaviour

and knowledge associated with successfully hunting kangaroos?

When O’Connell and Allen ask ‘why is Pleistocene Sahul

technology simple in some settings but complex in others’ , they

are actually mixing up stone or shell tools with fishing technology.

For the sake of having something concrete to observe,

archaeologists focus on the tools themselves rather than the

technology. Considering pursuit tools, the opposite of what

O’Connell and Allen predict is well-known. For recent hunter-

gatherer tool-kits, there is a strong negative correlation between

diet breadth and the complexity of both individual tools and

assemblages (Bamforth and Bleed 1997; Torrence 1989). The

reason for this pattern is that a wide range of complex and reliable

tools are required in situations where there is a high probability

of failing to acquire adequate resources. High risk is often, but

not always, correlated with specialised diets: environmental

parameters, such as seasonality, are also important. Where a

broad range of resources are targeted, risk of failure is generally

low and less time and energy are invested in tools. In these

situations generalised tools further reduce costs. I suspect the

same is true for processing and/or handling tools. Where the

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risk of failing to acquire sufficient resources is high, such as with

specialised diets, complex tools are required.

A further problem with the modelling in this article is

that the majority of tools used directly in subsistence tasks

during the late Pleistocene were made from plant materials

rather than stone. The primary role of flaked stone was for

manufacturing these tools rather than in pursuit or handling

of resources (stone points are only common later in time).

Since manufacture can easily be embedded in other activities,

the risk of failing to have the necessary tools prepared in

the required timeframe would have been low. Consequently,

the stone tools for producing other tools were fairly simple,

although we need better use-wear studies to investigate if and

how they were hafted.

Given the scarcity of evidence, I question O’Connell and

Allen’s emphasis on pelagic fishing, especially as a planned

subsistence activity, rather than as an adjunct to travel. If boat

technology was created and maintained primarily for voyaging,

then dropping a hook and line over the side would not have been

a costly or risky undertaking and so the unpredictable returns

would have been inconsequential. Given the paucity in late

Pleistocene contexts of fish remains and associated tools, it is

difficult to be certain about the relative contribution of pelagic

fishing to the diet, but I suspect that boats were primarily

designed for transport and exploration, and not for direct

capture of resources.

This brings up a major question raised but not answered

in the paper: despite the lure of high ranked resources lurking

just over the horizon, why did people risk deep-sea journeys?

Modelling the costs of search and pursuit takes us a long way

toward predicting human subsistence and consequences for

colonisation, but a more complete picture requires understanding

the factors behind taking and managing risk.

COLONISINg SAHUL

Mark W. MooreArchaeology and Palaeoanthropology, University of New

England, Armidale NSW 2351, Australia mmoore2@une.edu.au

A vague notion of ‘wanderlust’ seems to be the driving force in

many narratives about hominin migration (e.g. Dennell and

Roebroeks 2005), but, true to the zeitgeist, O’Connell and Allen

have shown us that wanderlust is all about food. The strength

of behavioural ecology is the explicit nature of the underlying

assumptions and the clear connection between forager theory,

predictive statements and archaeological evidence. Summarising

several optimal foraging models, O’Connell and Allen conclude

that optimising hominins are pulled from patch to patch by the

serial depletion of highest ranked resources. The logic of their

scenario is straightforward: the archaeological record shows

that humans colonised Wallacea and Sahul, and the theoretical

model stipulates that forager movement is linked to exploitation

of highest ranked prey, therefore colonisation was driven by the

pursuit of highest ranked prey. One might question whether

certain assumptions of optimal foraging models – for example,

that foragers have perfect resource knowledge and the perfect

ability to exploit it – would apply to the first wave of colonists

to cross the Wallace Line, but the successful colonisation itself

might be de facto evidence that the costs of imperfect knowledge

were not prohibitively high. O’Connell and Allen posit that,

after colonisation, movement between patches in pursuit of

highest ranked prey became the norm as foragers made nearly-

continuous readjustment to unstable climatic conditions.

Issues of colonisation rates and routes aside, the model

succeeds or fails by the prediction that the Pleistocene menu

was dominated by highest ranked prey. The data reviewed

by O’Connell and Allen are sketchy and, in most cases, the

regional and local subsistence resources surrounding early

archaeological sites are not sufficiently understood to warrant

informed scenarios of resource ranking (for instance, where are

the Australian megafauna?). Perhaps in light of this limitation,

O’Connell and Allen nod to the established tradition of

continent-wide generalisation and essentially treat all of Sahul

as if it were one patch. The continental zones with the greatest

density of highest ranked resources are termed ‘sweet spots’ and,

consistent with the model, the empirical evidence shows that

most early archaeological sites in Sahul are comfortably nestled

within them. However, it is not clear that the empirical pattern

identified by O’Connell and Allen is distinct from patterns

that might be predicted from the unspecified prior narratives

they term ‘minimalist’. The issue here is scale, and while the

data marshalled by O’Connell and Allen seem to support their

scenario, the true test will turn on detailed regional and site

specific reconstructions of palaeoclimate and subsistence.

O’Connell and Allen conclude their discussion with the

generalisation that simple technologies should correlate with

diets focused on highly ranked prey because greater investments

in finding food outweigh technological improvements in

obtaining it. This is a surprising observation, as many complex

forager technologies – particularly in North America and

Eurasia – are associated with the pursuit of highly ranked prey

species. Since a technological approach is an unarguable aspect

of hominin adaptation through the ‘extended phenotype’ (after

Boone and Smith 1998), a key challenge is to differentiate the

attributes of a technology that directly improve reproductive

fitness from those that are, at best, only indirectly related to

adaptation – what Bettinger (1991) has characterised as ‘adaptive’

and ‘adjustive’ traits, respectively.

For example, evolutionary models of flaked stone

technology implicitly assume that the tool as a whole was

adaptive and that inadequate tools directly compromised

fitness (Surovell 2009; Torrence 1986). But one might infer

from O’Connell and Allen that the only truly adaptive part

of a stone tool was the sharp edge, and the shape of the stone

bearing that edge – and thus the nature of the reduction

sequence that created the shape – was unimportant for

reproductive fitness, at least in the pursuit of highly ranked

prey. Most evolutionary narratives suggest that our early

hominin ancestors improved their fitness by creating sharp

edges for food procurement through least-effort flaking

(Ambrose 2001). This approach was exclusive among pre-

modern hominins for at least 1 my. The concern with tool

shapes that subsequently emerged among some (but not all)

modern human foragers was perhaps only an ‘adjustment’

within the extended phenotype and was only indirectly

related, or perhaps unrelated, to hominin fitness; direct fitness

requirements continued to be met through simple, least-

28 Number 74, June 2012

Forum

effort edge production similar to that seen among the modern

human colonisers of Sahul. Indeed, most complex stone

technologies worldwide, associated with a variety of foraging

strategies, included a least-effort reduction trajectory (often

under-analysed by archaeologists and sometimes ignored

altogether) alongside more complex ‘add-on’ approaches

to modifying stone shapes (e.g. Moore et al. 2009). Indeed,

once variables such as manufacturing skill, time investments

and ancillary costs of hafting are considered, it is rarely self-

evident that tools made by complex approaches significantly

improved the handling efficiency of the tools they augmented

(e.g. backed microliths vs flakes; tula adzes vs retouched

flakes, stone-tipped spears vs single-piece wooden ones) (cf.

White 1977). Perhaps the development of flaked stone tool

complexity beyond least-effort stone flaking had negligible

effects on the choices directly modelled by cultural ecologists,

and instead reflected adjustments to other parts of the

foragers’ extended phenotype.

ANd THE ANSWER IS 42 …

Judith FieldSchool of Biological, Earth and Environmental

Sciences, University of NSW, NSW 2052, Australia

judith.field@unsw.edu.au

The final line in the Restaurant at the End of the Universe quote

is a brilliant beginning to this interesting and ambitious paper

by O’Connell and Allen and speaks of the likely explanations

for the initial forays into, and expansion across, Sahul. That

‘42’ may be the answer to the meaning-of-life question, also

from this series, and perhaps the answer to the question

of human arrivals in Sahul – tells us something we already

know – that the fun is in the journey. I suspect all aspects of

this model will be debated and tested for a long time to come,

but the beauty of it lies in its breadth and the challenges that

will ‘feed’ a whole generation of archaeologists to come.

Having been engaged for some time in the ‘seemingly

eternal’ and faith-based debate about megafauna and its

relevance in the archaeological sphere, there are some issues

I would like to expand on that may contribute to the discussion.

O’Connell and Allen argue that one of the drivers for rapid

expansion was ‘serial depletion of high ranked prey’, which

on face value would support (and possibly revive) Flannery

and colleagues’ approach to the extinction process. The Steve

Wroe-coined phrase comes to mind – ‘spear-wielding hoards

hacking their way through startled megafauna’ – but this time

let’s throw in some of those extant species. If people arrived

on the northwest coast of the continent, the pickings may

have been sparse indeed and this alone would have accelerated

movement through the region. Entering via the Birds Head of

New Guinea may have been a different proposition altogether.

While the suite of animals and plants that were encountered

were entirely new, the ‘package’ of knowledge brought with

them may have enabled small populations to quickly adapt to

the new landscapes they encountered (as argued by Denham

et al. 2009). Certainly the discovery of Pandanus and yam in

the early occupation horizons from the Ivane Valley in the

eastern highlands of New Guinea points to this capacity

(Summerhayes et al. 2010). The observations by Geoff Hope

on Cyathea above the tree-line in this region also speaks of

important carbohydrates being readily accessible to, if not

exploited by, people in the recent past.

As always it is the preservational limitations of Australian

fossil sequences that inhibits a more fruitful exploration of

the ideas concerning exploitation of many animal species

in the Pleistocene record. What has become clear in the last

few years is the lack of evidence for a human-megafauna

association, despite the limited evidence for a temporal

overlap. Our scrutiny of the fossil record places only a handful

of megafauna still wandering around the landscape post-50 ka.

The spatial distribution of these remnant megafauna is

unclear and does not seem to be continuous across the

landscape. Yet this has not inhibited the supporters of human-

driven extinctions to push their particular barrow. The most

recent case is the report from Lynch’s Crater (Rule et al. 2012)

where they argue, on the basis of evidence from a sediment

core (analysing Sporormiella spores, charcoal and summary

diagrams of scleropyllous vegetation), that the extinction of

megafauna at 41 ka (where this date comes from in their paper

is unclear), drove changes in vegetation composition because

of ‘relaxed pressure’ on vegetation. Sporormiella spores are

used as a proxy for megafauna (but see critique by Feranec et

al. 2011). Despite these largely unproven assertions about the

timing of megafaunal demise, and the dismissal by Rule et al.

of climate change as an important factor, it now seems clear

to many that megafaunal extinctions cannot be considered an

archaeological question. For the most part, megafauna played

no significant role in the success or otherwise of colonising

populations in Sahul (Field and Wroe 2012).

I believe one of the important points that emerges from

this paper is the suggestion that we should broaden our gaze

when it comes to defining the particular conditions that

allowed/facilitated the movement of people to Sahul for the

first time. While to some extent we are still constrained by the

current sequences and dates for the earliest sites, O’Connell

and Allen challenge us to move away from the ‘lowest sea-

level moment’ when looking at the first arrivals. We are in

no doubt that the first Australians were behaviorally modern

and, as such, modes and routes of travel may have been

more complex than we can currently predict. One point that

has received little attention is the importance of access to

freshwater, a point raised by Horton (1984) some time ago as

it related to the faunal extinction process. It would seem that

the same principle may apply to colonising humans, especially

on the Australian continent. It is a fact that MIS-3 was not the

relatively stable climatic period as asserted by some authors

(e.g. Miller et al. 2005 and others), and clearly evident from

the Antarctic ice cores (EPICA Community Members 2006).

This instability must have been a determining factor in the

presence or absence of free water in the more arid regions

and also in the timing of movements across the Australian

continent. The unpredictability of sudden swings in climate

may have meant that the earliest archaeological records

reflected the necessarily ephemeral nature of occupation

across most landscapes.

So much to think about – this paper has given us a compass:

I look forward to seeing how it is used.

29Number 74, June 2012

Forum

RESPONSE

This paper developed as a Forum piece at the suggestion of

previous editor Sean Ulm, with continued positive input from

Lynley Wallis and Heather Burke. We thank them, and all the

contributors who took the time to respond.

Codding and Bliege Bird add an important dimension to

our argument by distinguishing the spatial (and by implication

temporal) scales at which foraging decisions operate – among

resources within patches, between patches within habitats, and

between habitats on continental and sub-continental scales.

Davidson, Dillehay, Horton and Keegan note that our model

makes no reference to considerations other than those related to

subsistence that might constrain movement into and across Sahul.

Our reductionist approach is intended to develop falsifiable

propositions about human behaviour in the distant past – it is

deliberately simplistic. It ignores social (except gender) and other

potential complexities, not because they were unimportant, but

because sidestepping them for the moment simplifies hypothesis

testing. We do not expect subsistence-related decisions to predict

or explain all aspects of past behaviour. Instead, we seek to

determine how much of that behaviour can be anticipated in

those terms, and to highlight what is not accountable in this way.

The exercise is intended to be iterative – we simply picked the

easiest, theoretically and empirically best-grounded place to start.

We recognise and share Cosgrove’s concerns about reconciling

data on different scales. To maintain simplicity and conserve

space this was not the place to pursue them. We use Oxygen

Isotope Stages and the like as familiar conveniences, but, with

Cosgrove, we believe that shorter-term climatic oscillations, like

ENSO – recognisable in human life spans – are the significant

modifiers of foraging behaviour.

Davidson and others note that the model assumes what

ecologists refer to as ‘complete’ knowledge of foraging

opportunities, and the costs and benefits of exploiting them.

The forager’s task of accumulating this knowledge is probably

less daunting than they imagine, especially at the resource and

patch scales on which short-term decision-making operates,

and especially with humans who can exchange knowledge

through language. Foragers’ abilities to assess the costs and

benefits of immediate subsistence-related opportunities and act

on them optimally is clearly indicated by the past four decades

of ethnographic research conducted within the framework of

behavioural ecology in Africa, the Americas and Australia. That

same research underlines foragers’ capacity to adjust to changes in

those constraints in real time. Davidson’s reference to Alyawarra

women’s use of O’Connell’s vehicle to reach and exploit high

ranked resources (mainly geophytes, never low ranked seeds)

in distant patches illustrates that ability. In archaeological

perspective, such adjustments, including those involving

previously unfamiliar resources, should be ‘instantaneous’. All

else being equal, we expect delays in the exploitation of new

opportunities to reflect ongoing assessments of economic and

ecological trade-offs, not slow learning. Tree and grass seeds

enter Australian diets late not because of a long-term lack of

relevant knowledge, but because the costs of exploiting them are

high relative to those associated with the use of many other foods.

Lilley chides us for what he sees as an inconsistent appeal

to ethnographic information. In our view, the question isn’t

whether to appeal to it, but how. Direct-historical analogies of

the kind once popular among Sahul archaeologists are now

often seen to be inappropriate, especially in late Pleistocene

settings. But rejecting any reference to human behaviour in the

present makes the archaeological enterprise entirely descriptive

and chronological. Simply accumulating more archaeological

data and ‘discussing’ them, the gambit Hiscock advocates

here and elsewhere, is a retreat to mindless empiricism and

baseless speculation, a Luddite strategy that sharply restricts

archaeology’s potential to reconstruct and explain the human

past. Our approach appeals to a uniformitarian theoretical

framework, capable of generating testable predictions about

many aspects of behaviour and shown empirically to be

applicable across a wide range of organisms, humans and fruit

flies alike (pace Horton). Among its most important virtues in

this context is its ability to generate predictions about patterns

in human behaviour unrepresented in ethnography. Codding

and colleagues’ (2011) recent work on the sexual division

of labour, specifically on the circumstances under which

men’s prey choices might be expected to trump women’s as

a determinant of residential site location in middle and low

latitude habitats, is a good example and one that we expect to

build on in future work.

On the relationship between technological complexity and

diet breadth: our sense of the global record, especially across the

late Pleistocene and Holocene, differs from the views expressed

by Torrence, Dillehay and, to some degree, Moore. Patterns in

Australian lithics are clearly consistent with our position, as are

those in, for example, western North American Paleoindian

vs Archaic contexts. Broader review is beyond us here, but

this difference of opinion may be at least in part a matter of

definition. For reasons stated in our paper and developed at

length in the sources we cite, we expect greater diet breadth to

be associated with increased complexity in handling technology,

defined as that connected with the post-encounter procurement

of prey, including all tools used in the pursuit, capture and

processing of those resources. We will explore this issue at greater

length elsewhere.

Minor points: (1) Our previous arguments for developed

watercraft did not rely heavily on the presence of pelagic fish

bones or fishing tackle in pre-LGM sites, but rather on the

need to maintain biologically viable colonising groups across

large distances. Nevertheless, the availability of such craft

would have facilitated pelagic fishing as a consequence; (2)

Our model is not simply an appeal to population pressure

as a catalyst for movement, but instead draws attention to

the complex interplay between unevenly spread populations

and resources, and the choices made about those resources

in relation to such movement; and, (3) Despite frequent

appeal to risk avoidance as a determinant of pre-European

technological diversity across Australia, the link between

the two remains poorly developed (White 2011). Recent

research from the perspective of behavioural ecology clearly

indicates that the significance of risk varies across habitats

and economies and (importantly) by gender (e.g. Hawkes and

Bliege Bird 2002). We look forward to further debate on this

issue. For the moment we side with Field and think the answer

to this and wider questions might still be ‘42’. We trust that

this piece opens a few doors.

30 Number 74, June 2012

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